Liquid crystal display devices have been used for many years. In the beginning, their uses have been concentrated in small appliance applications such as electronic watches and calculators. LCD's are now used in applications for instrument panel numerical displays and graphical displays. Advantages presented by LCD's are their inherent properties of small thickness, lightweight, low driving voltage required and low power consumption. As a consequence, more recent applications of color LCD's can be found in small screen television sets, notebook computer display panels and video camera view finders as replacements for conventional CRT's.
A liquid crystal display device can be made either a color unit or a black and white unit. The device may also be constructed as a reflective-type or as a transmissive type, depending on the light source used. Since liquid crystal molecules respond to an externally applied electrical voltage, liquid crystals can be used as an optical switch or as a light valve. A typical liquid crystal display cell arrangement is shown in FIGS. 1A and 1B.
Referring initially to FIG. 1A, wherein a liquid crystal display device 10 is shown. Liquid crystal display cell 10 is a single pixel which is constructed by two parallel glass plates, i.e. an upper plate 12 and a lower plate 14. Both the upper plate 12 and the lower plate 14 have a polarizing film 36 and 32 coated on its outer surface. The cavity 18 formed between the two plates 12 and 14 is filled with a liquid crystal material 20. One of the most commonly used liquid crystal material is of the twisted nematic (TN) type wherein the term twist refers to the tendency of the liquid crystal to form chains that rotate from one side 22 of the gap between the plates to the other side 24 of the gap. The degree of rotation can be controlled during the fabrication process.
As shown in FIG. 1A, light beam 28 passes through the polarizer 36 and then through the liquid crystal display cell 10 having its polarization direction rotated by following the physical rotation of the liquid crystal molecules 26. As shown in this simplified illustration, the polarizer 32 on the exit side 24 of the liquid crystal cell 10 is positioned such that it allows a rotated light beam 30 to pass through the polarizer 32. When viewed from the side of the polarizer 32, the pixel of the liquid crystal cell 10 thus appears clear, i.e. in a transmitting mode.
A transparent electrical conductor (not shown) such as indium-tin-oxide (ITO) is normally deposited on the inner surfaces of the glass plates 12 and 14. When a voltage is applied across the cell cavity 18 by addressing an appropriate line formed on each side of the cell, the liquid crystal molecules 26 reorient themselves to follow the applied electric field. The liquid crystal materials 26 are thus untwisted as shown in FIG. 1B. The passage of the untwisted light beam 34 is blocked by the exit polarizer 32 as long as the voltage is present. When the voltage is turned off (shown in FIG. 1A), the liquid crystal molecules 26 returns to their original state and the cell or the pixel becomes clear again. As previously stated, typical voltages and currents required to activate the liquid crystal molecules are relatively low making it an ideal candidate for incorporation in battery-operated equipment where low power consumption is essential. A typical twisted nematic (TN) liquid crystal cell used for small displays have a twist angle of 90°. More recently developed super twisted nematic (STN) material forms a twist angle up to 270° and thus allow higher contrast so that many pixel elements can be multiplexed in a single display.
While the liquid crystal display device 10 shown in FIGS. 1A and 1B is the transmissive type, liquid crystal display devices of the reflective-type are also used. In a reflective-type liquid crystal display device, one of the upper plate 12 and the lower plate 14 (shown in FIG. 1A) is replaced by a reflector plate which is light reflective and not transmissive. The reflector plate may be fabricated of a glass substrate with transistors or other active components built on top and coated with a metal reflective layer. In the reflective-type liquid crystal display device, the light source for illuminating the liquid crystal display is from the ambient such that a display is viewed in a reflective manner.
A drawback of the reflective-type liquid crystal display device is the noise signals reflected from the top, or the cover glass plate of the display device. In a conventional reflective type liquid crystal display device, the reflector plate and the top cover plate are parallel to each other. When an outside light source is used to produce an image in the liquid crystal device under the reflective principal, the light reflected from the reflector plate and from the top plate have the same reflective angle. Since the light reflected from the top cover plate does not produce the image formed in the liquid crystal display, only noise signals are produced with decrease the contrast of the display device. Furthermore, the noise/signal ratio of the device is also increased which affect the quality of images produced by the display device.
In recent years, the liquid crystal display panels have been more widely used in replacing the traditional CRTs in the electronics industry, and specifically, for the computer industry. In order for the LCD to completely replace the CRTs, various characteristics of the LCD panel must be improved which includes a wide viewing angle, better color definition and improved image clarity. At the present time, the twisted nematic LCDs are the most frequently used in the electronic and computer industry. Various efforts have been made on the improvement of viewing angles of the twisted nematic display panels, however, improvements are still needed in the color definition, in its dependence on the viewing position change and in the brightness uniformity when the liquid crystals are activated.
It is therefore an object of the present invention to provide a wide viewing angle LCD panel that does not have the drawbacks or shortcomings of the conventional LCD panels.
It is another object of the present invention to provide a wide viewing angle fringe field multi-domain aligned LCD that has significantly improved performance characteristics when compared to conventional LCDs.
It is a further object of the present invention to provide a wide viewing angle fringe field multi-domain aligned LCD that utilizes grid-like electrodes on at least one of the two substrate panels.
It is another further object of the present invention to provide a wide angle viewing fringe field multi-domain aligned LCD panel that includes a conductive grid of horizontal and vertical bars formed on a passivation layer and an electrically conductive layer on at least one of the two panel substrates.
It is still another object of the present invention to provide a wide viewing angle fringe field multi-domain aligned LCD panel that is vertically aligned with a liquid crystal material of negative dielectric anisotropy.
It is yet another object of the present invention to provide a wide viewing angle fringe field multi-domain aligned LCD panel with vertically aligned liquid crystal material of positive dielectric anisotropy.
It is still another object of the present invention to provide a method for fabricating a wide viewing angle fringe field multi-domain aligned LCD panel and vertically aligning the liquid crystal molecules to a negative dielectric anisotropy.
It is yet another further object of the present invention to provide a method for fabricating a wide viewing angle fringe field multi-domain aligned LCD panel by aligning the liquid crystal molecules vertically to a positive dielectric anisotropy.